In MIMO multiplexing, transmitting signals are assigned to a plurality of spatial streams; however, when the transmitting signals are assigned to the spatial streams in a fixed manner, variation in transmission quality can develop among the transmitting signals. To this end, conventionally association between transmitting signals and spatial streams has been periodically changed to equalize the transmitting signals in terms of transmission quality so that data transmission is less affected by channel estimation error resulting from variations in communication channels. For example, the following Nonpatent Document 1 describes a method of performing inter-eigenbeam interleaving for equalization of SINRs (Signal-to-Interference noise power Ratios) in an E-SDM (Eigenbeam-Space Division Multiplexing) system. In this system, MIMO spatial streams are assumed to be eigenbeams and inter-eigenbeam interleaving is performed by applying a single transmission power and a single modulation method to each of the eigenbeams.
Generally, when data is to be transmitted via transmitting antennas that differ from one another in quality of received signals transmitted via the transmitting antennas (e.g., SINRs), spectral efficiency can be increased by controlling any one of a transmission rate (by controlling a modulation order or an error-correction encoding rate) and transmission power for each of the transmitting signals depending on the quality.
Nonpatent Document 1: Uchida Daisei, Ohta Atsushi, Fujita Takashi, Asai Yusuke, Kagami Osamu, and Umehira Masahiro, “A Proposal of Inter-Eigenbeam Interleaving Scheme for Eigenbeam-Space Division Multiplexing for OFDM System”, Proceedings of the IEICE General Conference 2005, B-5-25.